Tests on major brands of bottled water have found that nearly all of them contained tiny particles of plastic.

Do you drink water from plastic bottles? Orb Media, a journalism organization, led a research study that discovered “an average of 10 plastic particles per litre, each larger than the width of a human hair.”

“Nestle told us its own internal testing for microplastics began more than two years ago and had not detected any “above trace level”. A spokesman added that Prof Mason’s study missed key steps to avoid “false positives” but he invited Orb Media to compare methods.

Gerolsteiner also said it had been testing its water for microplastics for a number of years and that the results showed levels “significantly below the limits for particles” set for pharmaceutical companies. It said it could not understand how Prof Mason’s study reached its conclusions.

It also said its measures exceeded industry standards but added that microparticles are “everywhere” so “the possibility of them entering the product from ambient air or packaging materials during the bottling process can therefore not be completely ruled out”.

Coca-Cola said it had some of the most stringent quality standards in the industry and used a “multi-step filtration process”. But it too acknowledged that microplastics “appear to be ubiquitous and therefore may be found at minute levels even in highly treated products”.

Danone said it could not comment on the study because “the methodology used is unclear” but added that its own bottles had “food grade packaging”.

It pointed out that there are no regulations on microplastics or a scientific consensus on how to test for them, and it also highlighted a much smaller German study last year that found plastic particles in single use bottles but not above a statistically significant amount.

PepsiCo said Aquafina had “rigorous quality control measures sanitary manufacturing practices, filtration and other food safety mechanisms which yield a reliably safe product”.

It described the science of microplastics as “an emerging field, in its infancy, which requires further scientific analysis, peer-reviewed research and greater collaboration across many stakeholders”.’